Electrical submersible well pumps are commonly used for pumping well fluid from wells producing oil, water and possibly gas. A typical submersible pump assembly has a rotary pump driven by an electrical motor. A seal section locates between the motor and the pump. The seal section has a flexible compensator element that reduces a pressure differential between lubricant in the motor and the surrounding hydrostatic well fluid pressure. The compensator element may be a tubular elastomeric bag, with an interior in communication with motor lubricant and an exterior in communication with well fluid. The upper end of the bag is secured by a bag clamp to an adapter on the upper end of the seal section.
The motor lubricant will expand with temperature. At the typical depths, the well fluid in most wells will be at a higher temperature than the temperature of the air surrounding the wellhead. Also, when the motor begins to operate, the lubricant temperature increases. Consequently, the compensator element will normally expand from its initial state.
Seal sections have check valves to expel excess lubricant if the interior pressure becomes too much greater than the hydrostatic well fluid pressure. However, even if the check valves are pre-set to a relatively low differential pressure, there still may be enough pressure in the bags due to thermal lubricant expansion to expand the bags up and over the bag clamp. When the bags are expanded around the bag clamp, it causes excessive stress in the area where the edge of the clamp contacts the bag.